The present invention relates to a modular expandable digital single-stage switching network in ATM (Asynchronous Transfer Mode) technology for a fast packet-switched transmission of information. The network has two types of fully switching, switching modules which are provided in each case with a plurality N of first inputs, a plurality N.times.L of expansion inputs, a plurality N or N.times.L of first outputs and a plurality N of expansion outputs. The switching modules are arranged in a matrix in such a way that solely basic modules are arranged in the last row of the matrix and in all preceding rows solely expansion modules are arranged. The expansion outputs of the switching modules are connected in each case to the first inputs of the switching modules in the following column, and the first outputs of the expansion modules are connected in each case to the expansion inputs of the switching modules in the following row, the switching modules having in each case on the first input side a header information filter for the purpose of route selection. The basic modules contain in each case a storage function (FIFO=First In/First Out).
A central element of future ATM broadband networks is the switching node. Since the required size of switching nodes can change as a result of traffic growth and new applications, there is a requirement for a simple expandability of switching nodes.
One solution proposed for the modular construction of a switching node ("KO switch") is described in a publication "IEEE Journal on selected areas in communications", Vol. SAC-5, No. 8, October 1987, p. 1274-1283. In the description below, this proposal will be compared with the switching network according to the present invention.
The prior art expansion concept is based on the so-called KO switch as an example of a broadband switching node. An N.times.N switching module (FIG. 1) consists in this case of N bus interfaces 10 (one for each output) containing in each case a filter 12, concentrator 14, shifter 16 and store 18. N lines are connected. In addition, N.times.L expansion inputs which lead to the concentrator 14 are provided. In the case of an expansion to 2N inputs and outputs, a further such switching module is additionally required. In addition, two switching modules whose bus interfaces 20 contain only a filter 22 and concentrator 24 (FIG. 2) are required. L intermediate lines are required per output between the (expansion) stages. The size of L depends here on the traffic load present and the required loss probability (e.g. L=8 with 90% traffic load and a packet loss probability of 10.sup.-6, cf. FIG. 5 in the publication cited). The overall number of lines between two switching modules 26, 28 is thus N.times.L (FIG. 3).